The present invention relates to method of providing a voice mail service in a mobile telephone network having a plurality of geographically dispersed voice mail storage units associated with respective network switching nodes.
The provision of voice mail services is well known in the art of telecommunications. Typically, a voice mail service allows callers to leave a recorded message for a subscriber who is unavailable at the time of the call. The called subscriber can then retrieve the messages at a later time.
A problem arises when voice mail services are provided in telephone systems, for example satellite mobile telephone systems and GSM cellular telephone systems, where a subscriber can roam over a wide area, possibly all over the world. In the case of a satellite mobile telephone system, the subscriber would access the system through different ground stations in different countries or on different continents. In the case of the GSM cellular telephone system and the like, the subscriber roves between services provided by different operators, for instance a UK-based subscriber might take his mobile telephone to Australia and use it with a network there.
In each of the these cases, the subscriber""s voice mail must be transferred over long distances each time it is accessed from outside the subscriber""s home location. Service providers often use other network""s lines for communication over long distances and this ad hoc transfer of voice mail does not promote cost-effective use of such lines. Furthermore, a subscriber who has roamed to another network must enter a long string of digits to access his voice mail in his home network. This has two disadvantages. Firstly, it is difficult for the subscriber to remember the sequence. Secondly, the voice mail service does not have the transparency which roaming is intended to provide.
Known satellite mobile telephone systems include the Inmarsat-M system, the IRIDIUM(trademark) system described in, for example EP-A-0365885, the ICO(trademark) system described in, for example, GB-A-2295296 and the ODYSSEY(trademark) system described in, for example, EP-A-0510789.
It is an aim of the present invention to overcome the afore-mentioned problems by providing for roving voice mail. In other words, a subscriber""s voice mail will follow him around.
According to the present invention, there is provided a method of providing a voice mail service in a mobile telephone network having a plurality of geographically dispersed voice mail storage units associated with respective network switching nodes, the method comprising transmitting the contents of a subscriber""s voice mail box in a first voice mail storage unit, associated with a first network switching node, to a voice mail box in a second voice mail storage unit, associated with a second network switching node, said transmission being in response to said subscriber""s mobile station registering with the second network switching node, wherein transmittal of the contents of the first voice mail box is effected in reponse to reception, by the first voice mail storage unit, of a voice mail transfer command, the command including a voice mail destination identifier identifying the second voice mail storage unit.
Since, the voice mail is transferred en bloc, a long-distance connection is not required each time a user accesses his voice mail away from his home location. Furthermore, the network control can arrange for the voice mail to be transferred in an economical manner, for instance to ensure that line capacity bought is fully used.
Preferably, the subscriber terminal apparatus is a mobile telephone and the network location of the subscriber terminal apparatus is determined during registration of the subscriber terminal apparatus with the network.
In the case of satellite mobile telephone systems, the user may be on occasion registered with a mobile satellite switching centre other than the one with which he is directly in contact. Accordingly, his voice mail would not be located at the closest node but merely one closer to him than the node which previously stored his voice mail.
Preferably, a method according to the present invention comprises maintaining a database of information relating to a plurality of subscriber mobile stations, the information including the network switching node with which the subscriber""s mobile station is registered and a voice mail box identifier; registering the subscriber""s mobile station at the second network switching node; updating the database record for said subscriber""s mobile station in response to said registration; and transmitting the voice mail transfer command to the first voice mail storage unit. More preferably, the voice mail box identifier stored in the database is altered to identify the second voice mail storage unit when the subscriber""s mobile station is subsequently deregistered with second network switching node.
Preferably, the voice mail transfer command is transmitted from the second network switching node.
The present invention finds application in a satellite mobile telephone system, in which case the network switching nodes are preferably comprised in satellite access nodes.
Preferably, a method according to the present invention includes compressing and/or encrypting the voice mail before it is transferred.
Preferably, the timing of the transfer of voice mail is dependent on network traffic level.
The present invention extends to a mobile telephone network including voice mail means operable according to any preceding paragraph of this section.